IV. VIRUSES

B. SIZES AND SHAPES OF VIRUSES

Fundamental Statements for this Learning Object:

1. Viruses are usually much smaller than bacteria with the vast majority being submicroscopic, generally ranging in size from 5 to 300 nanometers (nm).
2. Helical viruses consist of nucleic acid surrounded by a hollow protein cylinder or capsid and possessing a helical structure.
3. Polyhedral viruses consist of nucleic acid surrounded by a polyhedral (many-sided) shell or capsid, usually in the form of an icosahedron.
3. Enveloped viruses consist of nucleic acid surrounded by either a helical or polyhedral core and covered by an envelope.
4. Binal (complex) viruses have neither helical nor polyhedral forms, have irregular shapes, or have complex structures.

 

LEARNING OBJECTIVES FOR THIS SECTION

Viruses are infectious agents with both living and nonliving characteristics.

1. Living characteristics of viruses

a. They reproduce at a fantastic rate, but only in living host cells.

b. They can mutate.

2. Nonliving characteristics of viruses

a. They are acellular, that is, they contain no cytoplasm or cellular organelles.

b. They carry out no metabolism on their own and must replicate using the host cell's metabolic machinery. In other words, viruses don't grow and divide. Instead, new viral components are synthesized and assembled within the infected host cell.

c. The vast majority of viruses possess either DNA or RNA but not both.

Sizes and Shapes of Viruses

1. Size (see Fig. 1A, Fig. 1B, and Fig. 1C)

Viruses are usually much smaller than bacteria with the vast majority being submicroscopic (def). While most viruses range in size from 5 to 300 nanometers (nm) (def), in recent years a number of giant viruses, including Mimiviruses and Pandoraviruses with a diameter of 0.4 micrometers (µm) (def), have been identified.

To view a nice interactive illustration comparing size of cells and microbes, see the Cell Size and Scale Resource at the University of Utah. (Genetic Science Learning Center. (2010, September 2) Cell Size and Scale. Retrieved October 19, 2017, from http://learn.genetics.utah.edu/content/cells/scale/ )

YouTube movie illustrating Size Comparison of Microorganisms created by Gracia Alvaro Montoya, MetaBallsStudios (MBS), United Kingdom, Nov., 2017

 

2. Shapes (see Fig. 1A, Fig. 1B, and Fig. 1C)

a. Helical viruses (def) consist of nucleic acid surrounded by a hollow protein cylinder or capsid and possessing a helical structure (see Fig. 2A).

b. Polyhedral viruses (def) consist of nucleic acid surrounded by a polyhedral (many-sided) shell or capsid, usually in the form of an icosahedron (def); (see Fig. 2B).

• Transmission electron micrograph of Adenoviruses; courtesy of CDC.
• Transmission electron micrograph of poliomyelitis viruses; courtesy of CDC.
• Transmission electron micrograph of poliomyelitis viruses; courtesy of Dennis Kunkel's Microscopy.

c. Enveloped viruses (def) consist of nucleic acid surrounded by either a helical or polyhedral core and covered by an envelope (see Fig. 2C and Fig. 2D).

• Transmission electron micrograph of Hepatitis B viruses; courtesy of CDC.
• Transmission electron micrograph of an Influenza A virus; courtesy of CDC.
• Transmission electron micrograph of HIV; courtesy of CDC.
• Transmission electron micrograph showing envelope and glycoprotein spikes Coronaviruses; courtesy of CDC.
• Transmission electron micrograph of herpes simplex viruses; courtesy of Dennis Kunkel's Microscopy.

d. Binal (complex) viruses (def) have neither helical nor polyhedral forms, are pleomorphic or irregular shaped (see Fig 2E), or have complex structures (see Fig. 2F).

• Transmission electron micrograph of the bacteriophage coliphage T4. .

 

TPS Question

Concept Map for Sizes, Shapes, and Characteristics of Viruses